In a tense game of chicken, remarkable for its mix of petulance and audacity, congressional Republicans are threatening to halt U.S. aid to Ukraine—guaranteeing a Russian breakthrough and possible victory in that war—unless Democrats help pass a bill that all but locks down America’s Southern border.

If the impasse isn’t resolved by the end of next week, when Congress goes on recess until the new year, the Ukrainian army could run out of ammunition. President Joe Biden could resupply the arsenal from U.S. stockpiles without legislative approval, but the move would be temporary, and the signal sent—that Ukraine, and by implication other allies, can no longer count on U.S. support in a pinch—could be a holiday cork-popper for Russian President Vladimir Putin and all of our other adversaries.